1. Field of the Invention
The present invention relates to a process for the manufacture of a bearing unit that is applicable to rotating electric machinery and the like.
2. Related Art
A well-known type of bearing unit that is used commonly with rotating electric machinery is constructed so that a bearing that supports the rotating shaft in a freely rotatable manner is secured to a mounting member. FIG. 23 shows an example of the bearing that is used in such a conventional bearing unit, i.e., a sintered oil-retaining bearing; FIG. 24 shows an example of the motor that uses such a bearing.
In FIG. 23, the bearing indicated by 1 has not only a step 1d around the circumference but also a flange 1e on the circumference of one end portion. The diameters of inner peripheral portions 1a and 1c at opposite ends of the bearing 1 are worked to be equal to a specified finishing diameter and the inside diameter of the remaining middle portion 1b is adjusted to be larger than the diameter of the inner peripheral portions 1a and 1c at opposite ends. The difference between the inside diameter of the inner peripheral portions 1a and 1c at opposite ends and the inside diameter of the middle portion 1b is 2 .mu.m and more. The bearing 1 is a sintered oil-retaining bearing that is generally made of a sintered material and the process of its manufacture consists generally of the serial steps of powder compaction, sintering, a second application of pressure, and impregnation with a bearing oil. The difference between the inside diameter of the inner peripheral portions 1a and 1c at opposite ends of the bearing 1 and that of the middle portion 1b may be provided by various methods such as: (1) removing the sintered material from the middle portion by lathe turning; (2) deforming the sintered body by performing a special kind of compression, application of pressure, etc. in the second step of pressure application, and the like.
As shown in FIG. 24, the bearing 1 is secured to a mounting member 2 and a rotating shaft 4 is supported in a freely rotatable manner by means of the bore of the bearing 1. The mounting member 2 is a cup-shaped motor case; the bearing 1 is fitted through a hole in the center of the bottom of the mounting member 2 and the step 1d of the bearing 1 is crimped. The crimped portion and the flange 1e work together to pinch the mounting member 2 in the direction of its thickness, whereby the bearing 1 is secured firmly to the mounting member 2. The bearing 1 and the mounting member 2 form a bearing unit 3. The rotating shaft 4 is supported rotatably by the inner peripheral portions 1a and 1c at opposite ends of the bearing 1; since the middle portion 1b of the bearing 1 does not contact the rotating shaft 4, the advantage of small loss in torque will result.
The above-described prior art bearing unit has the following problems.
(1) The need to perform lathe turning or a special kind of compression, or pressure application or the like in the manufacture of the bearing 1 increases its cost. PA1 (2) The precision in fixing the bearing 1 or the parts precision of the bearing 1 and the mounting member 2 affect the precision in perpendicularity of the bearing 1 to the mounting member 2 in an adverse way. PA1 (3) Since the bearing 1 is generally made of a sintered material, the impregnated bearing oil may potentially leak out of oil holes in the circumference of the bearing 1 under the outward circumferential pressure exerted by the rotating shaft in action; to prevent this trouble, the oil holes in the circumference at the back of the face of the bearing 1 that supports the rotating shaft must be closed in a separate step but then the overall manufacturing process becomes complicated.